Twenty-eight juvenile Macaca fascicularis were immunized with subunit gp160, vaccinia-gp160 followed by subunit gp160, vaccinia-gp160 priming followed by subunit gp130 boosting, vaccinia-gag/pol plus vaccinia-gp160 priming followed by boosting with a mixture of gag/pol particle and gp160, vaccinia-gag/pol/env priming followed by pseudovirion boosting; or parental vaccinia virus as controls. These animals were first challenged intravenously with SIVmne E11S clone. Protected animals were boosted again and rechallenged with uncloned SIVmne. As reported last year, control animals were all infected, whereas animals that received both recombinant vaccinia virus priming and gp160 boosting showed partial protection (1/3 persistently infected, 1/3 transiently infected and 1/3 completely protected). Of the animals immunized with both envelope and core antigens, all 3 animals from one group (vaccinia-gag/pol/env priming followed by pseudovirion boosting) and 1/3 animals in the control group were completely protected. All but 14 animals were euthanatized last year. The remaining protected animals are being held for rechallenge studies.